Fix crash in destruction of standalone forms

If we just give the Dict to Object() it doesn't increase the ref
so on destruction we do one unref too much (because we had done one ref
too few) and crash
14 jobs for fix_crash_standalone_buttons in 8 minutes and 31 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #2217064
build

00:02:38

passed #2217059
build_android

00:00:59

passed #2217076
build_clang_libcpp

00:02:32

passed #2217068
build_clazy

00:02:54

passed #2217057
build_mingw64_fedora

00:02:43

passed #2217056
build_ubuntu_16_04

00:02:07

failed #2217054
build

00:00:13

failed #2217055
build_clang_libcpp

00:00:14

failed #2217070
build_clang_libcpp

00:00:13

failed #2217067
build_clang_libcpp

00:00:13

failed #2217069
build_clang_libcpp

00:00:14

failed #2217066
build_clang_libcpp

00:00:16

failed #2217065
build_clazy

00:00:53

failed #2217058
build_clazy

00:00:56